Bacteria accumulating on tumbler lids and rubber seals can reach up to 40,000 times the levels found on a toilet seat, according to experimental results. As reusable container use has grown, more people carry tumblers all day, but cleaning often amounts to little more than rinsing with water, experts note.
According to the medical community on the 16th, when Korea Water Resources Corporation tested water held in a tumbler, almost no bacteria were detected at first. But immediately after taking a single sip with the mouth touching the rim, the count rose to 900.
When left at room temperature above 20 degrees for three hours, the count reached 30,000, and after 24 hours it exceeded 40,000. In an experiment by U.S. water filter information company WaterFilterGuru.com, 20.8 million CFU/mL of bacteria were detected inside an ordinary tumbler. That figure is 40,000 times that of a toilet seat, four times that of a computer mouse, and twice that of a kitchen sink.
An analysis by research teams at Purdue University and James Madison University of 90 water bottles collected on campus also found heterotrophic plate counts of up to 8.03 million CFU/mL, and some samples even contained coliform bacteria, an indicator of hygiene conditions.
That far exceeds the 100 to 500 CFU/mL commonly used as a safety standard. A Singapore study published in the international journal "Journal of Environmental Engineering" also confirmed cases where bacteria in a tumbler holding boiled water increased to 1 million to 2 million CFU/mL after one day following a single sip.
Cleaning methods are cited as the reason bacteria increase this way. Experts explain that bacteria exist in the form of a biofilm, sticking to surfaces and creating sticky mucus to survive as a group, so they cannot be removed by rinsing with water alone.
Narrow, damp gaps like rubber seals, and structures difficult for cleaning tools to reach like straws, are cited as representative vulnerable spots. Some analyses note that tumblers with more sealed structures are harder to clean, making contamination more likely to be left unaddressed. The type of beverage held also has an effect.
Beverages containing sugar and protein, such as coffee, lattes, and protein drinks, become food for bacteria and multiply faster than plain water, experts explain. When left for long periods in environments with large temperature differences between indoors and outdoors in summer, the multiplication speed becomes even faster.
Experts recommend quickly emptying leftover beverages, adding neutral detergent or baking soda and shaking, then washing with hot water above 60 degrees. They advise separating the lid, rubber seal, and straw at least two or three times a week to clean into the crevices with a bottle brush and straw brush, and after washing, to completely dry the moisture before reassembling.
Some also point out that if odor or discoloration remains after washing, or if the rubber seal is cracked or stretched, it should be considered time for replacement.
